Process for the preparation of polylactam foams

ABSTRACT

AN IMPROVED PROCESS IS PROVIDED FOR THE PREPARATION OF POLYLACTAM FOAMS IN WHICH E-CAPROLACTAM OR A MIXTURE OF LACTAMS CONTAINING MORE THAN 50 MOL PERCENT OF E-CAPROLACTAM IS ANIONICALLY POLYMERIZED IN THE PRESENCE OF AN ALKALI CATALYST, A BLOWING AGEN AND A PROMOTER AT A TEMPERATURE OF ABOUT 100-180*C. THE IMPROVED PROCESS IS PARTICULARLY CHARACTERIZED BY THE USE OF A PROMOTER WHICH WHEN ADDED TO A MIXTURE OF LACTAM AND ALKALI CATALYSTS CAUSES THE MIXTURE TO SOLIDIFY DUE TO CRYSTALLIZATION WITHIN 3 MINUTES AND TO PRODUCE A POLYLACTAM HAVING A RELATIVE VISCOSITY OF AT LEAST 3 WHEN A CONVERSION REACHES EQUILIBRIUM. THE POLYLACTAM FOAMS OF THIS INVENTION EXHIBIT IMPROVED MECHANICAL AND CHEMICAL PROPERTIES IN COMPARISON WITH THE POLYLACTAM FOAMS OF THE PRIOR ART WHICH MAKE THEM ESPECIALLY USEFUL FOR THE MANUFACTURE OF LOW DENSITY ARTICLES REQUIRING RELATIVELY HIGH STRENGTH AND CHEMICAL RESISTANCE.

United States Patent O U.S. Cl. 260-25 N 8 Claims ABSTRACT OF THEDISCLOSURE An improved process is provided for the preparation ofpolylactam foams in which E-caprolactam or a mixture of lactamscontaining more than 50 mol percent of e-caprolactam is anionicallypolymerized in the presence of an alkali catalyst, a blowing agent and apromoter at a temperature of about 100-180 C. The improved process isparticularly characterized by the use of a promoter which when added toa mixture of lactam and alkali catalysts causes the mixture to solidifydue to crystallization within 3 minutes and to produce a polylactamhaving a relative viscosity of at least 3 when a conversion reachesequilibrium. The polylactam foams of this invention exhibit improvedmechanical and chemical properties in comparison with the polylactamfoams of the prior art which make them especially useful for themanufacture of low density articles requiring relatively high strengthand chemical resistance.

BACKGROUND OF THE INVENTION (1) Field of the invention This inventionrelates to an improved process for the preparation of polylactam foam.More particularly, this invention is concerned with the anionic fastpolymerization of e-caprolactam or mixtures of lactams to providepolylactam foams with a low density and improved mechanical and chemicalproperties.

(2) Description of the prior art Processes are disclosed in the priorart for the anionic fast polymerization of e-caprolactam using an alkalicatalyst. These processes are used to manufacture large shaped articlesdirectly from the monomer. Processes have also been suggested for thepreparation of poly-e-caprolactam foam in which the polymerization ofthe e-caprolactam is conducted in the presence of cell stabilizer and ablowing agent such as a volatile compound or a compound which decomposesto generate gas.

However, the properties, especially mechanical properties, ofpoly-e-caprolactam foams prepared by the prior art processes have beenunsatisfactory. It would be expected from properties of normal polyamideresins which have excellent mechanical properties, particularly inabrasion resistance and tensile strength and excellent chemicalresistance that the poly-e-caprolactam foams obtained by utilizinganionic fast polymerization would have similar properties. In the priorart foams however, the mechanical properties, such as tensile strengthand abrasion resistance and the chemical resistance were considerablylower than the values to be expected from properties of polyamideresins. The lower mechanical and chemical properties were especiallynoticeable in the case of low density foams. The prior art polylactamfoams whose apparent densities were below about 0.1 g./cm. would notretain the shape of a foam, and some foams even collapsed upon beingtaken out of the molds. For example, foams prepared at 120 C. using analkali catalyst and a promoter such as acetyl caprolactam or phenylisocyanate as 3,645,928 Patented Feb. 29, 1972 proposed in the prior arthaving an apparent density of below 0.05 g./crn. had a uniform cellstructure, but were mechanically very brittle, sometimes even collapsingupon taking it from the mold. The foams could easily be crumpled byhand, and as such were completely impractical. The foams prepared at 120C. using as a promoter, tolylene diisocyanate or diphenyl carbonatehaving an apparent density of about 0.05 g./cm. were more tenacious thanthe foams prepared by using phenyl isocyanate as the promoter. Yet thetensile strengths and flexural strengths were still low and the othermechanical properties were relatively low in comparison with variousother types of plastic foams, especially the thermosetting resin foamssuch as urethane, phenol and urea foams. The tensile strength normallyassociated with the polyamide resin was not present in the foamedmaterial. Each of the poly-e-caprolactam foams prepared using thevarious promoters suggested in the prior art by anionic fastpolymerization were unsatisfactory in mechanical properties.

An object of the present invention is to provide a low densitypolylactam foam having improved properties, especially mechanicalproperties and a process for the preparation of the foam.

SUMMARY OF THE INVENTION It has been found that the polymerizationactivity of the promoter has an important influence on the properties ofthe foams. More specifically, it has been found that in order to obtaina foam having a good cell structure and an apparent density below 0.1g./cm. it is necessary that the promoter when added at 120 C. to themixture of lactam and catalyst causes solidification of the mixturewithin 3 minutes, and preferably within 2 minutes. In addition, in orderto obtain a practical foam having satisfactory mechanical properties, itis necessary that the promoter employed results in the relativeviscosity of the polymer (measured in 98% concentrated sulfuric acid, ata concentration of 0.5% and at 25 0.), when the conversion reachesequilibrium being at least 3, and pref erably being insoluble in theconcentrated sulfuric acid.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to obtain satisfactorylow density foams it is indispensable in foaming that the generatingrate of the gas produced by the blowing agent and the polymerizationrate be in a proper relationship. If either rate is extremely large orsmall, it is not possible to obtain a foam having a satisfactorycellular structure and a low density. It has been found that in order toobtain a satisfactory foam having an apparent density below 0.10 g./cm.preferably below 0.05 g./cm. it is necessary to use a promoter whichwhen added at 120 C. to the mixture of lactam and alkali catalyst,causes solidification of the mixtures within 3 minutes, and preferably 2minutes. When a promoter satisfying this condition is used, thegenerating rate of a gas and the polymerization rate will be roughly inthe preferable relationship within the temperature range of 100-180 C.The solidification time will vary depending upon the concentrations ofthe alkali catalyst and promoter. There is an optimum concentration ofthe alkali catalyst and especially of the promoter which gives thelargest polymerization rate. When the concentration of either the alkalicatalyst or promoter is higher or lower than the optimum concentration,the polymerization rate is lowered. The polymerization activity of aparticular promoter is determined by measuring the time required for thesolidification due to crystallization of e-caprolactam usingpotassium-e-caprolactam as the alkali catalyst, and a concentration ofthe promoter which gives the largest polymerization rate when theconcentration of the alklai catalyst is 4 mol percent (based one-caprolactam). Normally, when the ration of the mol concentration of analkali catalyst to the mol concentration of functional groups of thepromoter is. in the vicinity of 1, the largest polymerization rate isobtained. It does not matter particularly that the polymerizationactivity of the promoter is large, because it is possible to control thepolymerization rate to the optimum by properly selecting thepolymerization temperature of the system and the concentration of thecatalyst system.

Even if a promoter satisfying the condition with regard to thesolidification time is used, it is still impossible to obtainsatisfactory foams having good mechanical properties. In order to obtaina foam having good mechanioal properties, it is further necessary thatthe promoter simultaneously satisfy the condition that the relativeviscosity of the polymer when the conversion reaches an equilbrium is atleast 3, and preferably the polymer should be insoluble in concentratedsulfuric acid.

The relative viscosity referred to in the present invention means theviscosity of a polymer when the conversion reaches an equilibriummeasured in 98% concentrated sulfuric acid at the concentration of 0.5%and a temperature of 25 C. When a promoter having a solidification timeof 3 minutes or less is used, normally by carrying out polymerizationfor about 30 minutes, the conversion will reach an equilibrium.

As lactams which may be employed in the present invention, particularattention is directed to e-caprolactam. In addition mixtures of at least50 mol percent, preferably 75 mol percent of e-caprolactam with otherw-lactams, can be employed. The w-lactams herein referred to are thosehaving 3-12 carbon atoms inside the lactam ring, such as pyrrolidone,piperidone, enanthlactam, caprylolactam and laurolactam.

The alkali catalyst employed by the prior art for the anionic fastpolymerization of lactams may likewise be employed in the presentinvention providing they have a sufiicient polymerization activity. Forexample, the alkali metal or alkaline earth metal such as sodium andpotassium, the hydride, alkylates having 1-10 carbon atoms, hydroxide,oxide, carbonate, aliphatic alcoholate having 1-10 carbon atoms andamide thereof are preferable catalysts. As specific examples thereof,metallic sodium, metallic potassium, lithium hydride, sodium hydride,potassium hydride, methyl sodium, ethyl potassium, butyl lithium,cyclohexyl sodium, methylcyclohexyl potassium, lithium hydroxide, sodiumhydroxide, potassium hydroxide, calcium hydroxide, sodium oxide, sodiumcarbonate, potassium carbonate, calcium carbonate, sodium ethylate,potassium methylate, sodium amide and potassium amide may be cited.

Upon producing a lactam basic salt by using the hydroxide, oxide,carbonate, alcoholate or amide, it is preferable to remove any water,carbon dioxide, alcohol and amine produced as by-products of thereaction with e-caprolactam or a mixture of e-caprolactam and otherw-lactams, prior to polymerization. The amount of the alkali catalystemployed should normally be 0.5- mol percent, and preferably 1-6 molpercent based on the lactam.

The promoter employed in the present invention must simultaneouslysatisfy the above noted conditions, that is the time from thecommencement of polymerizeration induced by the addition of the promoterat 120 C. until solidification due to crystallization must be within 3minutes, preferably 2 minutes and when the conversion reaches anequilibrium, the relative viscosity of a polylactam must be at least 3,and preferably insoluble in concentrated sulfuric acid. The promotersemployed in the present invention may be divided into two classes, thosecomprised of a single compound and those which are a composite of atleast two compounds.

One class of single compound promoters is the isocyanate compoundshaving at least 3 isocyanate groups bonded directly to an aromatic ring,and whose molecular Weight is ZOO-3,000, preferably 200-400. Specificexamples are 1-methylbenzene-2,4,6-triisocyanate,1,3-dirnethylbenzene-2,4,6-triisocyanate, 1,3,5-trimethylbenzene-2,4,6-triisocyanate, naphthalene-1,3,7-triisocyanate, biphenyl-Z,4,4-triisocyanate, diphenylmethane 2,4,4 triisocyanate, 3methyldiphenylmethane 4,6,4 triisocyanate, triphenylmethane 4,4',4"triisocyanate, a lower polymer of styrene-4-isocyanate (degree ofpolymerization 3-20), a reaction product of trimethylolpropane withtolylene diisocyanate (reaction product of molar ratio of 1:3) andpolymethylene polyphenyl isocyanate having an average of 3 or moreisocyanate groups per one molecule. The single compound promotersachieve the object of the present invention when used alone. It shouldbe appreciated that blends of these promoters may also be used and thateach of these promoters may also be used in combination with other typesof promoters.

The composite promoters of this invention consist of a combination oftwo types of promoters both of which when employed separately are notsuitable for employment in this invention. The first type of promoterwhen added by itself to the polymerization system at C. will causesolidification due to crystallization within 3 minutes. However, whenthe conversion reaches an equilibrium, the relative viscosity ofpolylactam will he less than 3. The second type of promoter results inthe polymer having the required relative viscosity but does not causesolidification in the required time,

Various known promoters belong to the first type of promoter employed inthe composite promoter of this invention. Specific examples of thesepromoters are as follows.

Acyl halides For example, aliphatic acyl halides having 2-10 carbonatoms or aromatic acyl halides having 7-15 carbon atoms such as acetylchloride, acetyl bromide, propionyl chloride, butyryl bromide, benzoylchloride, benzoyl bromide, o-toluyl chloride, terephthalyl chloride,fl-naphthoyl chloride and p anisoyl chloride.

Acyl lactams For example, aliphatic acyl lactams having 5-22 carbonatoms or aromatic acyl lactams having 10-25 carbon atoms such as acetylcaprolactam, benzoyl caprolactam, propionyl pyrrolidone and terephthalylpiperidone.

Isocyanates For example, aromatic isocyanates having 7-15 carbon atomshaving no more than 2 isocyanate groups in one molecule such as phenylisocyanate, phenylene diisocyanate, tolylene diioscyanate and naphthylisocyanate.

Carbonyl diimidazoles For example, canbonyl diimidazoles having 7-20carbon atoms such as 1,1-carbonyl diimidazole, 1,l-oarbonylbis(Z-methylimidazole) and terephthalyl diimidazole.

Aryl esters of carboxylic acid For example, aryl esters obtained fromaliphatic monocarboxylic acid or dicarboxylic acid having 2-10 carbonatoms or aromatic monocarboxylic acid or dicarboxylic acid having 7-15carbon atoms and phenols having 6-14 carbon atoms such as phenylacetate, phenyl propionate, phenyl benzoate, diphenyl terephthalate,(pentachlorophenyl) acetate, (Z-methylphenyl) acetate and B-naphthylbenzoate.

Halogenated formic acid esters For example, esters of a halogenatedformic acid and monoor di-alcohol having 1-9 carbon atoms or phenolshaving 6-14 carbon atoms such as ethyl chloroformate, phenylchloroformate, phenylenebis (chloroformate), ethylenebis(chloroformate), diethylenebis (chloroformate) and butyl bromoformate.

Aryl carbonates For example, aryl carbonates having 7-20 carbon atomssuch as diphenyl carbonate, di-p-toluylcarbonate, diethylene glycol bis(p-toluylcarbonate).

Acyl azides For example, aliphatic acyl azides having 2-10 carbon atomsor aromatic acyl azides having 7-15 carbon atoms such as acetyl azide,propionyl azides, benzoyl azi-de, terephthalyl diazide, O-toluyl azideand B-naphthoyl azide.

The foregoing are monoor di-functional promoters.

These known promoters heretofore used in the anionic fast polymerizationof e-caprolactam using an alkali catalyst, had solidification times at120 C. within 3 minutes, so they satisfy the condition for giving a foamof a high expansion ratio. However, they fail to satisfy the conditionfor giving a foam excellent in mechanical properties.

On the other hand, when certain known promoters are employed, foams areobtained which are excellent in mechanical properties. These promoterscause the relative viscosity of the polymer, when the conversion reachesan equilibrium, to be at least 3 and preferably cause the polymer to beinsoluble in concentrated sulfuric acid. These promoter compounds haveat least three functional groups. However, even though the promoters areat least trifunctional the compound of this type such as PCl P(NCO) andSi(NCO) are low in polymerization activity as shown in Example 1, Table1, Nos. 6, 7, 8 and 9. When polymerization is carried out at 120 C. forabout 30 minutes, the conversion does not reach an equilibrium and asufiiciently high relative viscosity cannot be obtained. These promoterscannot be utilized by themselves to obtain low density foams havingexcellent mechanical properties.

The composite promoters of the present invention are based on thediscovery that by using promoters in composite form, which when usedindividually, cannot achieve the object of the present invention.Superior promoters are obtained which can simultaneously satisfy thecondition for giving foams having excellent mechanical properties andlow density.

Generally, when additives such as promoters are used in composite form,in many cases the effect obtained becomes average of the effects wheneach promoter is used individually. However, in the present invention,both the polymerization rate and the relative viscosity of the polymervalues of the present invention, especially the relative viscosity ishigher than that obtained when each promoter is used individually. Thisis a distinct advantage of the mixed catalyst system of the presentinvention and it is a completely novel phenomenon not heretoforerecognized.

As explained above, as the promoters for achieving the object of thepresent invention, two kinds of promoter, one the single compound type,which even if when used alone, can achieve the object of the presentinvention, and other, the composite promoter are disclosed. The singlecompound type is generally somewhat unstable, difiicult to synthesize,accordingly the price is expensive and moreover some have possibilitydiscoloring the product. The promoter employed in the compositepromoters are commercially available and broadly used and accordinglythe composite promoters are somewhat more preferable.

The amount of the promoter employed in the present invention variesdepending upon the kind of alkali catalyst, the promoter and otherconditions. However, in order to obtain an effective polymerizationrate, an amount within the range of 0.110 mol percent, preferably 0.2-5mol percent is employed. In the case of using some promoters, forexample, esters such as phenyl acetate, phenyl benzoate or PO1 they havepossibilities of reacting with the alkali catalyst, or a lactam basicsalt, and converting said salt to an inert compound, therefore, whenthese promoters are used, it is preferable to make sufficiently high theconcentration of the lactam basic salt. In the present invention, incase the composite promoter of the type is used, there is no particularlimitation on the ratio of the two kinds of promoter, however, normallya molar ratio of 1:5 to 5:1 is used. In order to obtain a good foam, thepolymerization temperature in the process of the present invention ispreferably IOU-180 C., with IOU- C. being preferred. Namely, when thepromoter of the present invention is used, at the temperature range of100480 C., the polymerization rate and the generating rate of a gas areroughly in a preferable relationship. At the temperature below 100 C.,generally the polymerization rate is small, and at the temperature aboveC., the generating rate of a gas becomes excessive.

As a blowing agent generating an inert gas at the time ofpolymerization, known volatile type blowing agent and decomposition typechemical blowing agent are used, As examples of the volatile typeblowing agent, n-heptane, noctane, cyclohexane, methylcyclohexane,benzene, toluene, xylene, dioxane, dibutyl ether, triox ane and ligroinare used. As examples of the decomposition type blowing agents,azoisobutylonitrile and allyl azides may be cited. In the presentinvention, it is preferable to use a cell stabilizer such as a surfaceactive agent, for example, metal salts of stearic acid, silicones, metalsalts of phosphoric acid ester with an aliphatic alcohol which does notadversely affect the polymerization activity.

The polymerization and the foaming according to the present inventionmay be practiced in the presence of various modifiers which do notinterfere with the polym erization, for example, powder fillers, fibrousfillers, plasticizers, coloring agents, release agents, antioxidants andflame retardants.

In the process for the preparation of poly-e-caprolactam foam using thepresent invention, the polymerization and the foaming may be carried outin the same container. It is also possible to carry outprepolymerization with stirring, thereafter move the polymerizationmixture to another container or location and complete the polymerizationand the foaming. Stirring of the mixture during preparation of the foamis necessary for uniform dispersion of the promoter and for dispersingthe nuclei of cells through the mixture. To stir the mixtureconventional mechanical methods are employed. The stirring speed shouldbe 50-10,000 r.p.m., and preferably IOU-1,000 r.p.m. The stirring timevaries depending upon the polymerization conditions of the system,however, when the promoter of the present invention is used, a range offrom 10 seconds to 3 minutes, preferably from 20 seconds to 2 minutes isadopted. These operations are carried out normally under atmosphericpressure, however, it is also possible to carry out prepolymerizationunder a superatmospheric pressure, thereafter complete thepolymerization and the foaming under atmospheric pressure or a reducedpressure The poly-e-caprolactam foams obtained by the process of thepresent invention are open cell and have excellent mechanical strength,adiabatic properties, shook absorption properties, chemical resistanceand heat resistance. The foams are useful as an adiabatic material, acore material of a sandwich panel, flooring material, filters, shockabsorption materials, etc.

The present invention will be explained in more detail by the followingexamples, wherein percent means percent by weight.

EXAMPLE 1 A comparison was made of the results obtained with thecomposite catalysts of the present invention with the results obtainedusing each compound of the catalyst separately.

To molten e-caprolactam at 9095 C., particles of potassium hydroxidewere so added that the resultant potassium e-caprolactam concentrationwas 4 mol percent based on the e-caprolactam. The water produced as abyproduct was removed under a reduced pressure. 30 g. of thee-caprolactam solution containing the potassiume-caprolactam was placedin a test tube. The air inside the tube was replaced with nitrogen, andthe tube was heated to 120 C. When the temperature reached a constanttemperature of 120 C., a predetermined amount of the promoter was added.The test tube was then shaken until the reaction mixture became viscousand did not flow. The time from the addition of the promoter until thematerial did not flow was measured and recorded as a solidificationtime. After addition of the promoter, the polymerization was continuedfor 30 minutes. The test tube was then immersed in a methanol solutionof dry ice to stop the polymerization, and the conversion of theobtained polymer and the solution viscosity were measured. Theconversion was calculated from decrease of the weight after the polymerwas ground and extracted with boiling water for 6 hours and dried. Therelative viscosity 1 was measured in 98% concentrated sulfuric acid atthe concentration of 0.5% at 25 C. The results are shown in Table l.

EXAMPLE 2 In this example a further comparison is made of the compositepromoters of the present invention with other promoters.

100 g. of e-caprolactam solution containing 4 mol per cent ofpotassium-e-caprolactam was prepared as described in Example 1, wasplaced in a 70 mm. test tube. The air inside the tube was replaced withnitrogen. The

TABLE 1.INFLUENCE OF A PROMOTER ON POLYMERIZAT'ION Concen- Soliditrationfieation Conver- Relative (mol time sion viscosity No. Kind of promoterpercent) (min) (percent) t at Acetyl caprolactam 1. 5 0. 7 91 1. 5Phenyl isocyanate 1. 5 1. 6 92 L 5 Tolylene diisoeyauate. 1. 5 1.0 89 2.6 Diphenyl carbonate. 1. 5 1. 3 89 2. 9 Ethyl chloroformate 1. 5 0. 892 1. 7 P013 1. 7. 57 3.0 PCl3 0.5 6.5 8 1.6 P(BCO)3. 1.0 3.3 79 1.0S1(NCO) 1. 0 1'2. 0 3'2 2. 1 Acetyl caprolactam-PC-l3. 1-0. 5 0.8 90 3.0 Phenyl isocyanate 1-0. 5 1. 6 92 3. 2 Tolylene diisocyanateP(NCO)31-0. 5 1.2 90 Tolylene diisocyanate-SKNCO); 1-1 1. 2 88 Diphenylcarbonate-P(NC-O)3 1-0. 5 1. 5 85 4. 7 Ethyl choroformateP 013.... 1-0.5 0. 9 91 4. 2 16 Ethyl chloroiormate-PtNCOh 1-0. 5 0. 8 91 l Insoluble.

In Table 1, Nos. 1-5 are examples of promoters resulting insolidification times within 3 minutes at 120 C. Nos. 6-9 are examples ofat least trifunctional promoters resulting in polymers having relativeviscosities of at least 3 in concentrated sulfuric acid when conversionreaches an equilibrium. Nos. 10-16 are examples of the compositecatalysts of the present invention. As is apparent from these examples,the promoters of Nos 1-5 result in solidification times of within 3minutes at 120 C., however, when the conversion reaches an equilibriumthe relative viscosities are less than 3 which is low as compared withthe composie promoters used in the present invention, and they cannottherefore product foams having excellent mechanical properties. Thepromoters of Nos. 6-9 result in solidification times of more than 3minutes at 120 C.,

tube was heated to a predetermined temperature and 10% benzene and 1%dimethylsiloxane (Toray Silicone SH 200" cps), a cell stabilizer, wereadded. The mixture was stirred using an oar type blade, at 400 rpm. anda predetermined amount of a promoter was added. The resultant mixturewas stirred for the predetermined period, thereafter stirring wasstopped, the stirrer was removed and the system was foamed. The testtube was continuously heated for 30 minutes. Thereafter the test tubewas taken from the heating bath, left to cool. The foam was removed fromthe test tube. The conversion and the relative viscosity 1 of theprepared foam were measured by methods described in Example 1. Thetensile strength and the flexural strength of the foam were alsomeasured. The results are shown in Table 2.

TABLE 2.INFLUENCE OF A PROMOTER ON THE PHYSICAL 1 ROPERTIES OF A FOAMConeentra- Tempera- Stirring Apparent Conver- Relative Tensile Flexural2 tion (moi ture time density sion viscosit strength strength No. Kindof promoter percent) C (min.) (g./cm. (percent) m (kg./cm. (kg/cm!) 1 1.5 120 0. 6 0. 048 88 2 1. 5 120 1. 1 0. 049 92 3 1. 5 120 1. 0 0. 044 904 Diphenyl carbonate. 1. 5 120 1. 2 0.052 91 5 Ethyl ehloroformate 1. 5120 0. 5 O. 040 91 6 1. u 120 6. 0 44 7 1. 0 160 3.0 0. 120 87 8.. 1. 01'20 2. 5 0- 092 73 9 1. 0 120 10.0 34 10 Acetyl Gap 1-0. 5 120 O. 7 0.048 90 11 Phenyl isocyanate-P (NCO 1-0. 5 120 1. 0 0. 044 02 1 1-1 120l. 0 0. 040 13"-" 10. 5 120 1. 3 0- 048 91 14".. 1{). 5 120 0- 7 0.04515 Ethyl chloroformate-P (NC Ola- 1-015 1'20 0.5 (1.037 93 16 Ethylchloroiormate-Si(NC O)4 1-1 0.5 0. 044 91 1 Using a Dmnl1bell" type testpiece, measured at a tensile speed 0110 mun/min. 2 Using a 10 x 25 120mm. test piece, measured in accordance with .113 A9511.

3 N 01; foamed. 4 Insoluble.

and the polymerization rates are too small in order to In Table 2, thepromoters Nos. 1-5 are examples of a obtain low density foams. Moreover,when these pro- 7 promoter resulting in the solidification time ofwithin 3 nioters are used, even though polymerization is carried out at120 C. for 30 minutes the conversion does not reach an equilibrium.

However, in cases of the composite promoters using minutes at 120 (3.,giving low density foams which are very brittle and remarkably low inmechanical strengths. The promoters Nos. 6-9 are examples of at' leasttrifunctional promoters, which have a low polymerization rate acombination of promoters as shown in Nos. 10-16, the 75 with resultingfoams having a relatively high density.

Namely, upon using PCl and Si(NCO) the polymerization system does notfoam at 120 C. In the case of using PCl at 160 C. the polymerizationsystem is foamable,

however, a foam having an apparent density of below 0.1

By the method disclosed in Example 2, foams were prepared, and theconversions, relative viscosities 1 tensile 7 strengths and flexuralstrengths thereof were measured. The results were shown in Table 4.

TABLE 4.INFLUENCE OF A PROMOTER EXERTED ON THEPHYSICALPROPEBTIES OF AConcen- 1 Number of tration Tempera- Stirring Apparent Conver- RelativeTensile l Flexural I functional mol ture time density sion viscositystrength strength N0. Kind of promoter group percent) 0.) (sec.) (g./cm.(percent) 1 ,8 (kg/cm?) (kg/cm?) 1 PAPI 3 3 1 120 50 0. 042 89 5.0 7.2l-methylbenzene-2,4,6-trl- 3 1 120 40 0.046 89' 5.4 7.7

isocyanate. Triphenyl-4,4,4-tri- 3 1 120 40 0.050 90 6.5 8.8

isocyanate. 4 PAPI-Triphenyl-4,4',4- 33 0.5-0.5 120 50 0.043 88 5.0 7,4

triisocyanate. 5 Silicon tetraisocyanate 4 2 150 360 40 2.9 6Polycarbonate 3 1 30 50 0.050 80 2.3 1.4 2 7 1 Using a Dumbbell typetest piece. measured at a tensile speed of 10 mmJmin.

2 Measured in accordance With JIS A 9511 3 Polymetbylene polyphenylisocyanate, manufactured by SumitOmo Chemical Industry 00., Ltd. PAPI.

4 Insoluble. 5 Not foamed. Above 4.

In this example a comparison of the single compound promoters of thepresent invention with the other ordinary promoters is shown.

By the methods disclosed in Example 1, polymerizations were carried outand the solidification times, the conversions and the relativeviscosities 1 of using the single compound promoters of the presentinvention and the comparative prior art promoters were measured. Theresults are shown in Table 3.

In Table 5, Nos. 5-6 are examples of an at least trifunctional promoterother than those of the present invention and Nos. 1-4 are examples ofthe promoter of the present invention. When the promoters of the presentinvention are used, low density foams having high tensile strengths of5-7 l g./cm. are obtained. The same can be said of the flexuralstrengths, and it is apparent that when the promoters of the presentinvention are used poly-e-caprolactam foams are obtained which areexcellent in mechanical properties. No. 5 is an example of a promoterhaving such a low polymerization activity that a foam is not obtained.No 6 is an example of a promoter which fails to give a polymer of a highrelative viscosity, therefore the foam is inferior in mechanicalproperties.

EXAMPLE 5 0 g. of e-caprolactam solution containing 4 mol percent ofpotassium-e-caprolactam was charged in a 10 liter TABLE 3.INFLUENCE OF APROMOTER ON THE POLYMERIZATION Concen- Solidi- Number of trationfication Converfunctional (mol time sion No Kind of Promoter grouppercent) (min.) (percent) 1 3 1 9. 45 2.2. 3 1 1. 5 90 Insoluble. 31-methylbenzene-2,4,6-t y 3 1 1. 5 92 Do.Naphthalene-l,3,7-triisocyanate 3 1 1. 8 89 Do.Triphenylmethane-4,4',4"-triiso- 3 1 1. 4 90 Do.

cyanate. 6 Silicon tetraisocyanate 4 2 11. 5 35 2.4. 7 Polycarbonate 3 13.5 87 2.3.

1 Polymethylene polyphenyl isocyanate, manufactured by SumitornoChemical Industry 00., Ltd., PAPI. 2 Partially insolube in 98%concentrated sulfuric acid and viscosity could not be measured.

8 Panraito K-1300, manufactured by 'leijin Limited. 4 Above 4.

In Table 3, Nos. 1-5 are examples of a trifunctional promoter and Nos.6-7 are examples of an at least tetrafunctional promoter, of which Nos.2-5 are promoters of the present invention. When trifunctional promoterssuch as methyl silicon triisocyanate, silicon tetraisocyanate andpolycarbonate are used, the solidification times are more than 3 minutesand therefore they cannot be used as promoters to obtain low densityfoams. When the promoters of the present invention Nos. 2-5 are employedthe solidification times are short and polymers are of a high relativeviscosity, resulting in low density poly-ecaprolactam foams havingexcellent mechanical properties.

EXAMPLE 4 This example also compares the single compound procylindricalcontainer. The air inside the container was replaced by nitrogen and thecontainer was heated to a predetermined temperature. To said solution of10% of toluene and 1% of dimethylsiloxane (Toray Silicone SH 200) as acell stabilizer were added. While the resultant solution was beingstirred (400 r.p.m.), a predetermined amount of a promoter was added andthe stirring was continued for a predetermined time. Thereafter thestirring was stopped and the blade was taken out from the system and thesystem was foamed. After continuing the heating for 30 minutes, thecontainer was taken out of the heating bath and left to cool. Thereaftera foam was taken from the container. The results are shown in Table 5,each of the prepared foams has a low density moters used in the presentinvention with other promoters. and good mechanical properties.

TABLE 5 Coneentration Temper- Stirring Apparent (mol eture time densityNo. Kind of promoter percent) 0.) (min) (gJemfi) Terephthalylchloride-P613"; 0. 5-0. 5 125' 1.3 0. 048 1,1-carbonylbis(Q-methyl- 0.5-0. 5 125 0. 9 0. &4 imidazole)-P Cl:i. Y 1 Diphenyl terephthalate- 0.5,-0.5 125 1. 1 0 046 P (NC 0):. Pherryl acetate-P (NCO); 1-0. 5 130 0.9 0. 045 E%lg%6l18bl$(0hl0f0i0flllfit8)- 0.5-0. 5 130 0.7 0.039

3- L Etsl ylginebiswhloroiormate)- 0. 5-1 130 0.6 0. 039

' l 4. 7 Tolylene diisoeyanate-acetyl 1-0. 5-0. 5 130 0. 8 0. 042

caprolaetam-P C13. 8 Diphenyl carbonate-POI 0. 5-0. 5-0. 5 130 1. 2 0.046

P (NC 0):.

EXAMPLE 6 lactams containing more than 50 mol percent of e-capro- Inthis example a mixture of lactams is employed. Example 5 was repeatedwith the exception that a mixture of 90 mol percent of e-caprolactarncontaining 4 mol percent of potassium-e-caprolactam and 10 mol percentof w-lauryllactam was used in place of the e-caprolactam containing 4mol percent of potassium-e-caprolactam, employed in Example 5. Foamswere prepared. The results lactani is anionically polymerized ata'temperature of from about 100 to 1'80" C. in the presence of an alkalinecatalyst, a blowing agent, and a promoter, the improvement whichcomprises employing as the promoter a composition comprised of:

(a) a first compound selected from the group consisting of an aliphaticacyl halide having 2-10 carbon atoms; an aromatic acyl halide having7-15 carbon were ShOWI} m Table Each the P P F foams has atoms; analiphatic acyl lactam having 5-22 carbon at low density and goodmechamcal properties.

TABLE 6 Concentration Stirring Apparent (mol Temperatime density No.Kind of promoter percent) ture C.) (min (gjemfi) 1 Tolylenediisoeyanate-PCla 1-0. 5 130 1.2 0.043 Diphenyl carbonate-HNCO): 10.5130 1.4 0.047 3 PAPI t. 1 130 0.8 (1.039

EXAMPLE 7 atoms; an aromatic acyl lactam having 10-25 ca1' Example 2 wasrepeated with the exception that caprolactam solution containing 4 molpercent of sodiume-caprolactam obtained by using caustic soda particleinbon atoms; an aromatic isocyanate having 7-15 carbon atoms and havingno more than 2-isocyanate groups; a carbonyl diimidazole having 7-20carbon atoms; an aryl ester of an aliphatic monocarboxylic stead ofParticles Potassium hyfill'oxide Was p y so acid or dicarboxylic acidhaving 2-10 carbon atoms Foams were P Q as dlsclosed Examplfi The or anaromatic monocarboxylic acid or dicarboxylic sults are shown in Table 7.Each of the prepared foams id h i 7 15 carbon atoms d a h l h i has goodmechanical properties.

TABLE 7 Concentration Stirring Apparent (mol Temperatime density No.Kind of promoter percent) ture C.) (min) (g .lcmfi) 1 Tolylenediisoeyanate-PtNCO); l-O. 5 130 1. 5 0. 049 Ethyl chloroforrnate-PCI;1-0. 5 130 0. 8 0. 040 PAP 1 130 1.0 0. 041

EXAMPLE 8 This example shows the concurrent use of the single 6-14carbon atoms; an ester of a halogenated formic acid and monoordi-alcohol having 1-9' carbon atoms or a phenol having 6-14 carbonatoms; an

compound promoters of the invention and other promotcarbonate h i 7 2carbon atoms; an n. ers. Foams were prepared as in Example 5. Theresults phatic acyl azide having 2-10 carbon atoms and an are shown inTable 8. Each of the prep r foams aromatic acyl azide having 7-15 carbonatoms, and tamed in this example has a low density and good me- (b) aond compound l ted irom the grou onchanical properties. sisting of PClSi (:NCOM and P(NC-O) TABLE 8 Concentration Stirring Apparent (molTemperatime density No. Kind of promoter percent) ture C.) (mitt)(gJcml) 1 PAPI-acetyl caprolaritam- 0.5-1 0.8 0.042 2 1-0.5 120 0.60.040 3 o. 5-1 120 0. 7 0. 042 g 53 (11.8 0.044

. 4 6 1-methylbenzene-2,4,6- 0. 5-1 120 L diisoeyanate. 1 71-methylbenzene-2,4,GYtriisocyanatP/P(NC0);..- 10.5 120 1.2

-. The following is claimed:

2. The process according to claim 1, wherein said blend of lactarns iscomprised of e-caprolactam and wlactam having 3-12 carbon atoms insidethe lactam ring.

3. The process according to claim 1, wherein said alkaline catalyst is amember selected from the group consisting of sodium, potassium, and thehydride, alkylate having 1-10 carbon atoms, hydroxide, oxide, carbonate,aliphatic alcoholate having 1-10 carbon atoms or amide of sodium orpotassium.

4. The process according to claim 1, wherein the mixture contains 0.5-10mol percent of the alkali catalyst based on the lactam.

5. The process according to claim 1, wherein the molar ratio of thefirst compound to the second compound is 6. The process according toclaim 1, wherein 0.1- mol percent of the promoter is added.

7. The process according to claim 1, wherein the polymerizationtemperature is 100130 C.

8. In the process for the preparation of a polylactam foam, wherein apolymerizable member selected from the group consisting of e-caprolactamand a blend of lactams containing more than mol percent of s-caprolactamis anionically polymerized at a temperature of from about to C. in thepresence of an alkaline cata lyst, a blowing agent, and a promoter, theimprovement which comprises employing as the promoter a compositioncomprised of:

References Cited UNITED STATES PATENTS Black 260-78 P Fuller 260-78 LFuller 260-25 W Giberson 260-78 L Bayerlein et al. 260-25 W ISteeIy260-78 L Hyde a. 260-78 L MURRAY TILLMAN, Primary Examiner M. FOELAK,Assistant Examiner US. Cl. X.R.

25 260-37 R, 78 L, 78 P

